As a link plate forming a roller chain used in a timing drive system in an internal combustion engine and a manufacturing method thereof, for example an invention shown in FIGS. 5 and 6 has been developed by the present inventors (see Japanese published application No. JP2005-021911). It is noted that FIG. 6 is an enlarged view of a working region shown by VI in FIG. 5.
Namely, as shown in FIG. 5, a band-shaped steel plate (sheet) H drawn out of a supply roll is intermittently, sequentially fed into a link plate punching metal mold D based on pilot holes R. Then a pair of pin holes 510 and 512 are first punched on the center line of the band-shaped steel plate H by pin-rough punching molds d4. Then as shown in FIG. 6 in detail, while leaving cutting margins K at both longitudinal ends of a link plate 500, see FIG. 5(a), the link plate 500 is punched by a plate rough-punching working mold d5 of a shape having a pair of semicircular end portions forming left and right half arcs 514 and 516, see FIG. 5(b), which are concentric with and spaced outwardly from the pin holes 510 and 512 respectively, and a pair of upper and lower straight line portions 518 and 520 connecting both end portions at the opposite ends of the pair of left and right half arcs 514 and 516.
When rough-punching is performed, a rough surface is produced having a “sag” along the edge of the work piece where the punch first meets the workpiece (This shown in an exaggerated form in FIG. 8(a) at 10.), and/or travel of the punch below the sag 10 produces a rupture rough surface 20 (shown in exaggerated form in FIG. 4(b) at 116), and/or where the punch passes beyond the work piece, a burr 30 can be generated on worked cross-sections as shown in FIG. 8(a). Accordingly, by using a plate shaving mold S4 of a shape, which is slightly larger than a contour of the plate rough-punching mold d5, as shown in FIG. 6, outer peripheries of the roughly-punched link plate is subjected to shaving so that roughly punched surfaces are slightly shaved down to obtain smooth sheared surfaces (shaved surfaces) 40 as shown in FIG. 8(b). In FIG. 8(b) an object shown by the reference numeral 50 denotes a shaved scrap. It is noted that although in FIGS. 8(a) and 8(b) the shaved surface and roughly punched surface are exaggeratedly depicted, the shaved thickness DS is actually about 0.1 mm.
It is noted that “the shaving” in the present invention means a fabrication (secondary processing) in which by the use of a shaving mold having a contour slightly larger than a contour of the peripheral portion of a punched plate. By punching a band-shaped steel plate with a working mold (generally called a “punch”) during rough punching referred to as primary processing as shown in FIG. 8(a) the peripheral portion of the band-shaped steel plate to be punched is punched to shave small amount of peripheral portions of the punched plate as shown in FIG. 8(b) so that any sag 10, rupture rough surface 20 and burr 30 generated during the rough punching with the punch are removed to improve the surface roughness and surface accuracy of the roughly punched peripheral portions.
Next, the inner circumferential surfaces of the pin holes 510 and 512 are subjected to shaving by shaving molds S3 (FIG. 5). And finally cutting margins are cut with a roughly punching mold d6 to complete a link plate 500 (see for example Japanese Laid-Open Patent Publication No. 2005-21911 (pages 5 to 7, FIGS. 2 and 3)).
Further, a less expensive plate shaving mold has been also proposed, and is shown at S5 in FIG. 7. Since a tensioner lever or a guide lever comes into sliding contact with the plate, shaving of only the pair of upper and lower straight line portions of a link plate are subjected to shaving for smoothness.